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          <th colspan="3" align="center">Working with primitive types </th>
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          <div>
            <h2 class="title" style="clear: both"><a id="stl_primitive_rw"></a>Working with primitive types </h2>
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          <dt>
            <span class="sect2">
              <a href="stl_primitive_rw.html#id1600210">Storing strings</a>
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      <p>
    To store simple primitive types such as <code class="literal">int</code>,
    <code class="literal">long</code>, <code class="literal">double</code>, and so forth, an
    additional type parameter for the container class
    templates is needed.  For example, to store an <code class="literal">int</code>
    in a <code class="classname">db_vector</code>, use this container class:
</p>
      <pre class="programlisting">db_vector&lt;int, ElementHolder&lt;int&gt; &gt;;</pre>
      <p>
    To map integers to doubles, use this:
</p>
      <pre class="programlisting">db_map&lt;int, double, ElementHolder&lt;double&gt; &gt;;</pre>
      <p>
    To store a <code class="literal">char*</code> string with <code class="literal">long</code> keys, 
    use this:
</p>
      <pre class="programlisting">db_map&lt;long, char*, ElementHolder&lt;char*&gt; &gt;;</pre>
      <p>
    Use this for <code class="literal">const char*</code> strings:
</p>
      <pre class="programlisting">db_map&lt;long, const char*, ElementHolder&lt;const char*&gt; &gt;;</pre>
      <p>
    To map one const string to another, use this type:
</p>
      <pre class="programlisting">db_map&lt;const char*, const char*, ElementHolder&lt;const char*&gt; &gt;;</pre>
      <p>
    The <code class="methodname">TestVector::test_primitive()</code> method demonstrates more of these examples. You can find this method implemented in the dbstl test suite.
</p>
      <div class="sect2" lang="en" xml:lang="en">
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            <div>
              <h3 class="title"><a id="id1600210"></a>Storing strings</h3>
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        <p>
    For <code class="literal">char*</code> and <code class="literal">wchar_t*</code> strings,
    <code class="methodname">_DB_STL_StoreElement()</code> must be called
    following partial or total modifications before iterator movement,
    <code class="literal">container::operator[]</code> or
    <code class="literal">iterator::operator*/-&gt;</code> calls.  Without the
    <code class="methodname">_DB_STL_StoreElement()</code> call, the modified
    change will be lost. If storing an new value like this: 
</p>
        <pre class="programlisting">*iterator = new_char_star_string;</pre>
        <p>
    the call to <code class="methodname">_DB_STL_StoreElement()</code> is not needed.
</p>
        <p>
    Note that passing a NULL pointer to a container of
    <code class="literal">char*</code> type or passing a
    <code class="classname">std::string</code> with no contents at all will insert
    an empty string of zero length into the database.
</p>
        <p>
    The string returned from a container will not live beyond the next
    iterator movement call, <code class="literal">container::operator[]</code> or
    <code class="literal">iterator::operator*/-&gt;</code> call.
</p>
        <p>

    A <span class="bold"><strong>db_map::value_type::second_type</strong></span> or
    <span class="bold"><strong>db_map::datatype_wrap</strong></span> should be used
    to hold a reference to a <code class="literal">container::operator[]</code>
    return value. Then the reference should be used for repeated 
    references to that value. The *iterator is of type 
    <code class="literal">ElementHolder&lt;char *&gt;</code>, which can be automatically converted to a
    <code class="literal">char *</code> pointer using its type conversion operator.
    Wherever an auto conversion is done by the compiler, the conversion
    operator of <code class="literal">ElementHolder&lt;T&gt;</code> is called.  This
    avoids almost all explicit conversions, except for two use cases: 

</p>
        <div class="orderedlist">
          <ol type="1">
            <li>
              <p>
            The *iterator is used as a "..." parameter like this: 
        </p>
              <pre class="programlisting">printf("this is the special case %s", *iterator);</pre>
              <p>
            This compiles but causes errors.  Instead, an explicit cast
            should be used:
        </p>
              <pre class="programlisting">printf("this is the special case %s", (char *)*iterator);</pre>
            </li>
            <li>
              <p>
                For some old compilers, such as gcc3.4.6, the *iterator cannot be 
                used with the ternary <code class="literal">?</code> operator, like
                this:
            </p>
              <pre class="programlisting">expr ? *iterator : var</pre>
              <p>
                Even when <span class="bold"><strong>var</strong></span> is the same
                type as the iterator's <code class="literal">value_type</code>, the
                compiler fails to perform an auto conversion.
            </p>
            </li>
          </ol>
        </div>
        <p>
    When using <code class="classname">std::string</code> or
    <code class="classname">std::wstring</code> as the data type for dbstl
    containers — that is, <code class="classname">db_vector&lt;string&gt;</code>,
    and <code class="classname">db_map&lt;string, wstring&gt;</code> — the
    string's content rather than the string object itself is stored in order
    to maintain persistence.
</p>
        <p>
    You can find example code demonstrating string storage in the
    <code class="methodname">TestAssoc::test_char_star_string_storage()</code> and 
    <code class="methodname">TestAssoc::test_storing_std_strings()</code>
    methods. These are available in the dbstl test suite.
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